This invention relates to sewing machines and to cutting systems for same. More particularly, this invention relates to a pneumatically actuated, computer-controlled cutting system for a cam pattern sewing machine.
Some conventional mechanically driven sewing machines use continuously run motors which drive a belt system to turn clutches which move a shaft. A cutting cam moves an arm shaft, a spring and a tension release in synchronization with the hook and needle. The cutting cam, arm shaft, and spring thus position the movable cutting blade to first and second positions for trimming both the upper needle thread and lower bobbin thread.
In mechanically driven pattern tacker systems, a pattern cam determines the specific timing and movement of a cutting blade. A pattern cam 200 of the kind used in most conventional mechanically driven machines is shown in FIGS. 1a and 1b. The conventional pattern cam 200 has a first face 205 (FIG. 1a) and a second face 210 (FIG. 1b), each face defining a stitching groove 215 for determining a sewing pattern. The first face 205 of the conventional pattern cam is substantially circular, and the second face 210 defines a stopping lug 218 and a stopping groove 223. The stopping lug 218 engages a lever (not shown) or some other member to engage a cutting cam. The stopping groove 223, which is necessary in some conventional pattern tackers to guide a roller, is disadvantageous because the stopping groove 223 results in a thin, weak stitching groove all 225 where the stitching groove 215 of the second face 210 is close to he stopping groove 223. Thin portions of the stitching groove wall 225 re designated at 227 in FIG. 1b.
Some conventional electronically controlled pattern tacking sewing machines use a stepping motor to move a workpiece plate in "X" and "Y" axis directions. When cutting is to be performed, the motor is slowed through a series of electronic signals to insert a roller, which has a standard rod connected to linkage, into a slot within the cutting cam. Once the roller is in the slot, the movable cutting blade is moved to trim both the upper needle and lower bobbin threads of the sewn work piece.
Operation of the cutting cam in either a conventional mechanical pattern tacking sewing machine or a conventional electronically controlled pattern tacking sewing machine requires many parts including a roller to follow the cutting cam, levers, and, in conventional mechanically controlled sewing machines, clutches. Such parts can be expensive to assemble and properly maintain. Further, a spring returns the cutting blade to a home position. Such spring mechanisms are a relatively weak and unreliable means for returning the cutting blade to the home position. If the blade does not fully return because of a weak spring, the needle may hit the blade, possibly breaking the needle, the blade, and the needle plate.
In some cutting systems for conventional mechanical sewing machines, if the sewing machine is stopped mid-cycle (e.g., for an emergency) then the cutting blade might still be driven to cut the thread. If the needle happened to be down when the sewing machine was stopped, the cutting blade would hit the needle, possibly breaking the needle, the blade, and the needle plate. Also, the clutches and other cutting assembly parts might require significant readjustment prior to use following a collision of the cutting blade and the needle.
In some cutting systems for conventional electronic and conventional mechanical sewing machines, a tension release mechanism is connected to the cutting cam. Being connected to the cutting cam results in the tension release lever being activated at the same point in every cycle. Further, changing the tension release mechanism timing requires adjustments of many parts.
In some conventional mechanically or electronically controlled sewing machines, the cutting blade remains in the second or cutting position until a few stitches of a subsequent sewing cycle have been completed. Following those stitches, the cutting blade is retracted. This is disadvantageous because it requires more thread from the bobbin.
In some conventional pattern tackers, in order to change the speed of the motor, the motor had to be changed or the puller and belt had to be changed. Such changes are inefficient.